(function (doc, win) {
      var docEl = doc.documentElement,
      resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
      recalc = function () {
             var clientWidth = docEl.clientWidth;
             if (!clientWidth) return;
             docEl.style.fontSize = 20 * (clientWidth / 320) + 'px';
      };
      if (!doc.addEventListener) return;
      win.addEventListener(resizeEvt, recalc, false);
      doc.addEventListener('DOMContentLoaded', recalc, false);
})(document, window);